Traditional semiconductor devices based on control of the flow and the density of electric charge (e.g., electrons or holes) are nearing a point where every new step towards miniaturization or towards increasing the operating speed demands new technology and huge investments. In particular, as semiconductor devices become smaller (e.g., near nanometer scale) or need to operate at faster speeds, the heat that electrical currents generate in semiconductor devices becomes a greater problem. Additionally, semiconductor devices are now reaching sizes at which previously ignored quantum-mechanical properties such as spin are significant. Dealing with these quantum-mechanical properties can be a challenge in the design of traditional semiconductor devices, but such quantum mechanical properties also provide the potential for alternative mechanisms for device operation.
One important quantum property of electrons is their intrinsic spin. The spin of an electron gives the electron an intrinsic magnetic moment that can interact with electromagnetic fields. The spin interactions of electrons therefore provide a potential mechanism for operational devices, and such devices can be very fast and potentially generate less heat than do traditional devices. The field of spintronics has thus arisen from efforts to develop fast solid-state devices such as transistors, amplifiers, and magnetic sensors of nanometer proportions that use the spins or the associated magnetic moments of electrons.
S. Datta and B. Das in “Electronic Analog of the Electrooptic Modulator,” Applied Physics Letters, Vol. 56, p. 665, proposed a spin transistor based on the spin-orbital coupling of electrons to a gated electric field. Other types of spintronic devices are now sought to provide fast operation, low heat generation, and scalability down to nanometer sizes.